Evacuated variable condensers



Feb. 17, 1970 A. P. O. COLLIS EVACUATED VARIABLE CONDENSERS 2 Sheets-Sheet 1 Filed April 29, 1968 INVENTOR 41w w Q/umo mm W x Ifimw ATTORNEYS Feb; 17, 1910 I A. P, o. cam 3,496,430

EVACUA'I'ED VARIABLE CONDENSERS Filed April 29. 1968 2 Sheets-Shea 2 M /%M$ W ATTOR NEYS United States Patent 3,496,430 EVACUATED VARIABLE CONDENSERS Alec Peter Orme Collis, Essex, England, assignor to English Electric Valve Company Limited, London, England, a British company Filed Apr. 29, 1968, Ser. No. 725,104 Claims priority, application Great Britain, May 17, 1967, 22,923/ 67 Int. Cl. H01g /02, 1/08 US. Cl. 317-245 7 Claims ABSTRACT OF THE DISCLOSURE An evacuated condenser includes, in addition to the normally provided bellows used to vary the capacity of the condenser whilst maintaining a good degree of vacuum, auxiliary bellows which are arranged so that electrical current in the normally provided bellows is greatly reduced. The current flows instead in the auxiliary bellows which are positioned to connect the same parts of the condenser as the normally provided bellows, but which are made easy to cool.

The invention is illustrated in and explained in connection with the accompanying drawings. FIGURE 1 illustrates in a simplified schematic half sectional view the invention as applied to a condenser which is of the kind referred to and is, apart from certain added parts which are provided by this invention and will be specified hereinafter, of known construction, and FIGURE 2, shows a preferred constructional modification of the bellows. Like references denote like parts in the two figures.

Referring to FIGURE 1, the condenser therein shown has two electrode systems 1 and 2, of which the former is fixed and the latter is movable. The electrode systems are co-axial and each consists of a number of concentric cylindrical electrodes of such diameters that, when the moving system 2 is moved in the axial direction towards the fixed system 1 its cylindrical electrodes penetrate into the spaces between the cylindrical electrodes of said fixed system, the capacitance in any position of motion depending, of course, upon the depth of penetration. The fixed system 1 is carried by a metal end plate member 3 and the moving system by a metal end plate member 10. These parts 3 and 10, together with the metal parts 5 to 9 inclusive, the ceramic or glass insulating parts 11, 12 and 13, the axially situated metal bellows 14 and the pinch off which is inside and is covered and protected by the metal part 4 combine to provide an envelope the space within which is evacuated. In the drawing an additional bellows is ,shown above the bellows 14 and the part 9 has a hole providing communication to the interior of this additional bellows. The said additional bellows and the said hole are, however, provided by this invention and are not preseiit in the known construction now being described. They should, therefore, be ignored for the moment and the drawing regarded as though the bellows 14 were the only bellows and the member 9 had no hole through it.

3,496,430 Patented Feb. 17, 1970 Endwise movement of the electrode system 2 is obtained, in the embodiment illustrated, by rotating an axially situated longitudinally restrained threaded spindle 15 on which is a nut member 16 which is constrained against rotary motion and which, when the spindle is rotated, moves endwise to transmit motion in the axial direction via the part 17 to the plate 10 carrying the moving system 2. The part 18 serves as a guide for the endwise sliding part 17. Other means for moving the electrode system 2 endwisee.g. a hydraulic drive from the linearly moving piston of a hydraulic cylinder-could be used. As will be apparent from the drawing, when the moving system 2 moves endwise in one direction or the other, the bellows 14, inside which the part 18 is situated, is expanded or contracted, maintaining the vacuum with atmospheric pressure on the inside and vacuum on the outside of it. Movement of the moving system 2 away from the system 1 is limited by a stop 19 and mounting rings 20- are provided for mounting the whole condenser.

A known condenser as so far described has the defect that, when it is used in a high power radio frequency circuit, e.g. as a tuning condenser in such a circuit, the maximum current which it can carry is undesirably limited by heating of the bellows 14 by the radio frequency currents flowing therein. The path of radio frequency current flow is indicated in the drawing by the various curved arrows. Because of radio frequency heating of the bellows 14 it would be desirable to make them of some such metal as copper which is of good electrical and thermal conductivity but such metals do not have the mechanical properties necessary to give the bellows a reasonably long life and accordingly, in practice, metals of better mechanical properties but of relatively low electrical conductivity have to be used for the bellows. If a metal of better electrical conductivity, e.g. copper, or Phosphor bronze clad with copper, is used for the bellows 14, the useful life of the bellows is reduced or the cost of the condenser is substantially increased, or both. -If it is sought to overcome the difficulty by increasing the diameter of the bellows 14 and thus decreasing the radio frequency current density through it and therefore its power loss, there is the defect that the said bellows must be made stronger and stiffer because, of course, the total atmospheric force to be withstood thereby increases with increase in diameter and bellows of greater stiffness are more difiicult to make of long life. Moreover the greater the atmospheric force the more the force which has to be exerted to adjust the condenser and increase in the latter force is a serious defect especially in the case of remotely controlled condensers. To cool the bellows by cooling air or water is diflicult to accomplish satisfactorily because much of the interior space of the bellows is already occupied by parts of the drive mechanism for the moving electrode system.

According to this invention an evacuated variable condenser of the kind referred to comprises, in addition to the normally provided bellows which is included in and forms part of the vacuum envelope of the condenser, at least one auxiliary bellows providing mechanical connection between the moving electrode or electrode system of the condenser and a fixed part thereof, said auxiliary bellows providing a relatively low resistance path or paths for current flowing through the condenser.

In a preferred arrangement in which the said normally provided bellows is located round the axis of the condenser and surrounds part of a mechanism for moving the moving electrode or electrode system, there is a plurality of auxiliary bellows extending parallel to said normally provided bellows and arranged in a ring around the same, the auxiliary bellows and the normally provided bellows mechanically connecting the same two parts of the condensers.

Preferably means are provided for preventing the flow of current through the normally provided bellows so that substantially the whole current is carried by the auxiliary bellows. Such means may conveniently consist of an insulating ring 23 or like member which forms part of the evacuated envelope of the condenser and is interposed between one end of the normally provided bellows and the adjacent condenser part with which said bellows mechanically connects. A second insulating ring 24 may be additionally or alternatively provided between the other end of the normally provided bellows and condenser part 9 with which said bellows mechanically connects.

If desired, means may be provided for cooling the auxiliary bellows by cooling fluid (preferably air or water) fed to the interior thereof. Thus, for example, one of two condenser parts mechanically connected by the auxiliary bellows may have a hole or holes each leading from outside the evacuated space to the interior of an auxiliary bellows so that cooling fluid may be fed to said interior.

Referring again to FIGURE 1, in order to describe the parts which are added in accordance with this invention, the said parts consist of a number of auxiliary metal bellows of good conductivity which extend parallel to the normally provided bellows 14, are arranged in a ring round said bellows 14, and mechanically connect the same parts 9 and 10 which are connected by the said bellows 14. Thus, for example, there might be fourauxiliary bellows, 90 apart, only one of which appears in the drawing and is referenced 21. As indicated in the drawing the part 9 has a hole 22 opposite each auxiliary bellows and putting the interior of said bellows in communication with the outside atmosphere. It forced cooling is required cooling air or water may be pumped into the interior of each auxiliary bellows through the appropriate hole 22.

Preferably current is excluded from the normally produring assembly of the whole device to be replaced by another without scrapping the whole device. It has the further advantage that it enables each bellows to be tested as a unit before assembly in the device.

Referring to FIGURE 2, the bellows 21 is made as a complete unit with a screwed end piece 21 at one end (the moving end) adapted to screw with a threaded hole 10 in the part 10 (FIGURE 1). The same method of construction is used for the bellows 14 (not shown in FIGURE 2).

In manufacture each bellows is made as a complete unit and tested. If found satisfactory it is then inserted into the envelope and the screwed end piece (21 in the case. of bellows 21) is screwed into the threaded hole for receiving it. The bellows seal is then completed by argon welding to the part 9 (or to a member carried thereby).- In the event of later failure of a bellows it is easy to make a light cut over the weld, unscrew the faulty bellows, replace it by a new one, screw it in and re-weld.

I claim:

1. An evacuated variable condenser comprising two electrodes or electrode systems within an evacuated envelope part, a first bellows which enables the vacuum to be maintained while allowing one electrode or electrode system to be moved in relation to the other in order to vary the capacitance by a capacitance adjustment drive which is operable from outside the evacuated space, said first bellows being located round the axis of the condenser and surrounding part of a mechanism for moving the vided bellows by providing an insulating ring member 24 and/ or 23 to form part of the evacuated envelope between one end of the bellows 14 and the adjacent member 9 or 10 (as the case may be).

As will be seen, with this improved arrangement the electrical current through the bellows 14 is at least much reducedif said bellows 14-is insulated at one end it is reduced to zero-and much, if not all, of the current is taken through the auxiliary bellows which are easy to cool and do not need to be particularly stifi or expensive. In practice the bellows 14 and 21, though differently shown in FIGURE 1, would usually be similar and as shown for the bellows 14 in FIGURE 1. The provision, in accordance with this invention, of auxiliary bellows has the advantages (1) that the current density therein can be made low, the more there are of them the lower the current density therein can be made and (more importantly) (2) the auxiliary bellows can easily be cooled, if required, because they are open to atmosphere and unencumbered by drive mechanism. The r invention enables the maximum current which the condenser can handle satisfactorily without excessive power loss or reduction of useful life to be substantially increased in relation to that of a known comparable condenser.

moving electrode or electrode system, and a plurality of auxiliary bellows,said plurality of auxiliary bellows extending along different axes parallel to the axis of said first bellows and arranged to surround the same, said plurality of auxiliary bellows providing relatively low resistance paths, bypassing the first-mentioned bellows, for current flowing through the condenser.

2. A condenser as claimed in claim 1 wherein said first bellows and said plurality of auxiliary bellows mechanically connect the same two parts of the condenser.

3. A condenser as claimed in claim 2 including means for preventing the flow of current through said first bellows whereby substantially the whole current is carried by said plurality of auxiliary bellows.

4. A condenser as claimed in claim 3 wherein said means for preventing the flow of current comprise an insulating member which forms a part of said envelope part of the condenser and is interposed between one end of said first bellows and the adjacent one of said two condenser parts which said first bellows mechanically connects.

5. A condenser as claimed in claim 4 wherein said means for preventing the flow of current further comprise a second insulating member which forms a part of said envelope part of the condenser and is interposed betweenthe second end of said first bellows and the other adjacent one of said two condenser parts which said first bellows mechanically connects.

6. A condenser as claimed in claim 4 wherein said plurality of auxiliary bellows is provided with cooling FIGURE 2 shows, to a different scale from FIGURE I 1 and only so far as is necessary to an understanding thereof, a constructional modification of the arrangement of the bellows14 and 21-it is shown for the bellows 21 placed. It also has the advantage of facilitating manufacture by enabling a bellows found faulty or damaged only in FIGURE 2 but would be adopted for both belmeans.

7. A condenser as claimed in claim 4 wherein each bellows is a complete, removable and replaceable unit.

References Cited UNITED STATES PATENTS 3,270,259 8/1966 Oeschger 317- 245 X E. A. GOLDBERG, Primary Examiner U.S. Cl. X.R. 

